My invention relates generally to construction machines or earthmovers, and in particular to scrapers towed behind a tractor and used principally for excavation and hauling purposes. Even more particularly, my invention is directed to some improvements in a push-pull coupling capable of selectively connecting and disconnecting such tractor-scraper units so that they may operate either in tandem or as independent units.
The push-pull coupling for a tandem arrangement of tractor-scraper units, as heretofore made, typically comprises a push block and pulling hook arranged at the rear of a front tractor-scraper unit, and another push block and bail on the front of a rear unit, as taught in Campbell et al U.S. Pat. No. 3,434,738, issued Mar. 25, 1969. The two push blocks made contact with each other when the tractor-scraper units are coupled together in pushing relation, and the shock produced at this juncture is reduced as by a pair of spring groups which can be associated with either of the push blocks.
The noted U.S. patent, however, reveals no means for reduction of the shock that is produced also upon engagement of the pulling hook by the bail, that is, upon establishment of a pulling relation between the tractor-scraper units. This deficiency is an inevitable result of the fact that the pulling hook and bail are both rigidly connected to the respective frameworks of the front and rear tractor-scraper units. As a consequence, the frameworks directly suffer the shock caused upon engagement of the pulling hook by the bail.